Black Bean and Sweet Potato Chilli with Cocoa

Why it works

The unsweetened cocoa is not a novelty. A spoonful adds bitterness and depth that reads as long-cooked, and it brings flavanols studied for blood vessel function into a savoury dish where nobody expects them. The substance of the bowl is black beans and sweet potato, which together deliver 15 grams of fiber a serving, most of it the soluble kind that slows digestion and feeds gut bacteria. Chipotle contributes smoke and capsaicin, and the acid from lime at the end lifts the whole thing. This is also the clearest example in the library of a dish that improves with storage: the starch from the sweet potato continues to thicken it, and the spice loses its raw edge overnight, so a Wednesday portion is better than a Sunday one.

Ingredients

• 2 × 400 g tins black beans, drained and rinsed
• 600 g sweet potato, cut into 2 cm cubes
• 400 g tin chopped tomatoes
• 1 onion, diced
• 3 garlic cloves, minced
• 2 chipotle chillies in adobo, chopped, plus 1 tbsp of the sauce
• 1 tbsp natural unsweetened cocoa powder
• 2 tsp ground cumin
• 1 tsp dried oregano
• 500 ml low-sodium vegetable stock
• 1 tbsp olive oil
• Lime wedges, coriander, and plain yogurt to serve

Method

1. Warm the oil in a heavy pot and cook the onion over medium heat for eight minutes until soft and beginning to colour.
2. Add the garlic, cumin, oregano, chipotle, and cocoa, and stir for a minute until it smells toasted rather than raw.
3. Add the sweet potato, beans, tomatoes, and stock. Bring to a simmer and cook uncovered for 35 to 40 minutes, until the sweet potato is tender and the liquid has reduced to a thick sauce.
4. Crush a few of the sweet potato cubes against the side of the pot with a spoon. That is what thickens a chilli without flour.
5. Taste, add lime until it tastes bright rather than heavy, and serve with coriander and a spoonful of yogurt.